Creep resistant non-austenitic steels



United States Patent CREEP REQISTANT NON-AUS'IENITIC STEELS Geoffrey T. Harris, Sheflield, and Henry C. Child, Rotherham, England, assignors to The Birmingham Small Arms Company Limited, Birmingham, England, a company of Great Britain No Drawing. Filed Aug. 24, 1959, Ser. No. 835,415 Claims priority, application Great Britain Aug. 27, 1958 .9 Claims. (Cl. 75-126) is a continual demand'for improved creep-strength.

Examples of developments in this field are to be found in British Patents Nos. 638,110; 658,115; 730,272; 733,146

and 796,733. In these patents alloys are disclosed con- "ice The following is a preferred narrower range of elements according to the invention any one or all'of which may be substituted for the corresponding element or elements in the ranges given above: 1 l

Percent Carbon 0.08-0.2 Nickel 0-2 Chromium 10-13 Cobalt 5-10 Tungsten and/or molybdenum 0-2 Niobium and/or tantalum 4 1.5-2.5 Vanadium 0-1.5 Boron 0-0.02 Nitrogen .02-0.09 Aluminium 0-0.1

1 Must be in excess of tungsten and/or molybdenum.

Preferably the total of tungsten or molybdenum is below 1% and, still more preferably, below 0.5%.

Where no intentional nitrogen addition has been made, additions of the deoxidiser, zirconium, are desirable in amounts of up to 0.2%.

The following examples illustrate. the invention, the alloy .W. 684 not being in accordance with the present taining from about 9% to about 20% chromium and, in invention but being inserted for purposes of comparison:

0 Mn 51 N1 Cr 00 W Mo V Nb B N w.5s4. 0.1a 1.2 0.3 0.8 10.5 5 1.0 1.0 0.5 0.5 0.01 0.07

addition, one or more of molybdenum, tungsten, vana- In each of these alloys iron and impurities constituted the dium, niobium, tantalum or titanium,- As deoxidisers manganese and silicon are usually added. Nickel may also be incorporated, usually in amounts up to about 5%. For most practical purposes it is desirable that the carbon content should be below about 0.3%.

In the prior work little, if any, attention has been given to the relationship between tungsten and/ or molybdenum on the onehand and niobium and/or tantalum on the other hand. Whilst not advancing any particular theory, we have found, and this forms the basis of the present invention, that in alloys of the kind in question improved creep strength may be obtained if the content of niobium and/or tantalum exceeds the content of tungsten and/or" molybdenum and the latter may be omitted entirely. Further, in muchof the work'in this field, vanadium has been regarded as an essential alloying constituent. Alloys daccording to the present invention need not necessarily.

contain vanadium. Nickel may also be omitted. -Ac-" cordingto a feature of this invention alloy steels of the kind referred to comprise the following ingredients within the ranges specified, the percentages being by weight:

.. ..Percent Carbon 0.01-0.2 Nickel 0-4 Chromium 9-15 Cobalt 3-15 Tungsten and/or molybdenum .1.....;.. 0-2 Niobium and/or .tantalum 1 1-3 Vanadium 5 5 3 Boron 0-0.5 Nitrogen. 0-0.1 Aluminium -Q- Y Must: be in excess of tungsten and/0r molybdenum. together with deoxidisers, e.g., manganese 0.1-2% and silicon 0.1-1%, and iron and impurities which form the an e balance. When tested at 8 tons at 600 C. these four alloys reached the total plastic strain in hours indicated below: c

from 1200 C. and tempered at 650 C.

It was found that still furtherimprovements could be achieved by tempering at higher temperatures, e.g., by tempering at 700 C. The creep strength of W. 862 based on a criterion of 0.1% total plastic strain in 100 hours at 600 C. was 23 tons/sq. in; This might be compared with similar creep strength of 10 tons/ sq. in.

. for W. 684.

Satisfactory creep strengths which would be acceptable for many purposes, however, could. be obtained by solution treating over a wide range of temperatures from 1000 C. to 1250 C. and tempering 'inithel'range 550 to750C.

The influence on thejcreep strength, of some of the various alloying. additions, is tabulated below.

The basic alloy was W. 862, the composition of which is given above.

The composition of the alloys was kept to this specification, except, of course, for the element which was being varied.

In order to indicate the efiect of heat treatment, two

results are given forsome alloys, one in heat treated.

Condition A and the other in Condition B or C.

Condition A:

/2 hr. at 1200 0., oil quenched, 211 3- 522591 #99,!1...

Condition B:

/2 hr. at 1200" (3., oil quenched,

2 hrs. at 700 C., air cooled. Condition Effect of the ratio of the carbide formers when total kept at 3% [Tested under 17 tons/sq. in. at 600 0.]

[Tested under 20 tons/sq. in. at 600". Q]

Percent B Percent strain. in

l mhr. at'1'200'f 0,511 quenched, 5 Percent strain 2 hrs. at 725 C., air cooled. Nb, M0+w, in 100 hours Efiect 0f niobium tantalum Alloy percent" percent? percent];

A B [Stress to give 0.1% in 100 hours at 600 0.] Z

- 2. 52.1 0.451 "0.32? 0. 23 V I Stressmtons/sq.u1. 2.33 I -'0.'48:.' -'0.'27- 0.20 Yemeni 1. 90 0.40: 0.15 0.11 e 2.2 0.8 0.20' 0.10 1 A 0 1.75. 0.85, 0.15 10.00 1.5 0:3' 0:32 0.50 1 1.98 1.07, 0.12 .000 117 "15' 22 It may be seen that whilsta small addition of vanadium has a beneficial effect on the creep strength at 600 C. E echo .cobalt H a v the properties of the vanadium free alloy lfi C'Stlll-SllOW a [Stress i 100 hours at 600 substantial improvement over :previous alloys with low "niobium content. It is also evident that a high tungsten Alloy Percent streSsmtms/Sq'm' and molybdenum content is beneficial, although, of 00 7 course, this content still remains lower 1 than the total A B content of niobium and tantalum. I 1 23 25 The "following areexarnples of alloy *steels :according 2 9' 8 28 to theinvention in'which tungsten and molybdenum are 14 0. 12 16 absent the alloyW. 954 (not=being= acc0rding to the invention) being included for'theipurposes of comparison:

Fe and 0 "Mn Si Ni Cr Go V Nb Al B N imtpuri- 1. 21 0.3 .08 10.5 5.0 3.0 0.1 0.01 0. 07 Balance. 1.2 5 0.13 .05 10.5 5.0 3.0 3.0 0.1 0.01 0.07 D0. 1.2 05s, 08 10.5 5.0 1.5 1.5 0.1 0.01 0.07 D0.

Efiect ofzcarbon .onralloysicontaining 7%:C0 Creep -strengths -Heat treatrnentr 5 Tesbed-under 20'tons/sq; in. at 600 0.]

[ 40 1hr. at-1200 6.,"011 quenched Pement smmm 2hrs. at 6S0-C., air cooled Percent 100 hours Testing: "8 tons/sq. in., ,at 600 C. n v Q B V .Tlmetn. :Time to Strain, 5 a 0.05%; V 0.1%, .percent 0.13 0.10 0.065 hrsi I hrs. 0.10 0. 29 0.28 4 0. 0a 0.53 0. a5

Eflect of boron 100"hours Alloy .such valloysare.

7 A B a 1 I Percent 27 52 0.01 0125 0107 9 0.019 0:13, 0.09 I a a a a N 0:045 $0.13- 0. 17 v 7 .5 7 Cl. 11.,6. 10, 5 ,Mn 0S6 10.8 1W 2 0.5 Effect of nitrogen 1g: v Y 0.0.5: 055 [Tested under 20 tons/sq. 1n.,'-at 600 0.] Fe and impurities Balance Balance "Percent strain in We claim:

1. Non-austenitic alloy steels consisting by weight essentially of 0.01 to 0 .2% carbon, nickel up to 4%, chromium 9-15%, cobalt 315%, one or more materials selected from the group consisting of tungsten and molybdenum up to 2%, one or more materials selected from the group consisting of niobium and tantalum 13% and in excess of the total material or materials selected from the group consisting of tungsten and molybdenum, vanadium up to 3%, boron up to 0.05%, nitrogen up to 0.1%, aluminium up to 0.1%, and the balance essentially iron.

2. Alloy steels according to claim 1 in which up to 2% vanadium is present.

3. Alloy steels according to claim 1 containing one or more materials from the group consisting of manganese and silicon, said manganese being present within the range of 0.1 to 2%, and said silicon being present in the range of 0.1 to 1%.

4. Alloys according to claim 1 in which the tungsten content is less than 1%.

5. Alloy steels according to claim 1 in which the tungsten content is less than 0.5%.

6. Alloy steels according to claim 1 in which the molybdenum content is less than 1%.

7. Alloy steels according to claim 1 in which the molybdenum content is less than 0.5%.

8. Non-austenitic alloy steels consisting by weight essentially of 0.08 to 0.2% carbon, nickel up to 2%, chromium 10-43%, cobalt 510%, one or more materials selected from the group consisting of tungsten and molybdenum up to 2%, one or more materials selected from the group consisting of niobium and tantalum 1.5 to 2.5% and in excess of the total material or materials selected from the group consisting of tungsten and molybdenum, vanadium up to 1.5%, boron up to 0.02%, nitrogen 0.02 to 0.09%, aluminium up to 0.1%, and the balance essentially iron.

9. Non-austenitic alloy steels consisting by weight essentially of 0.01 to 0.2% carbon, nickel up to 4%, chromium 9-15%, cobalt 3-15 one or more materials selected from the group consisting of tungsten and molybdenum up to 2%, one or more materials selected from the group consisting of niobium and tantalum 13% and in excess of the total material or materials selected from the group consisting of tungsten and molybdenum, vanadium up to 3%, boron up to 0.05%, aluminium up to 0.1%, and the balance essentially iron with up to 0.2% zirconium as a deoxidiser.

References Cited in the file of this patent UNITED STATES PATENTS 1,711,484 Armstrong May 7, 1929 

1. NON-AUSTENITIC ALLOY STEELS CONSISTING BY WEIGHT ESSENTIALLY OF 0.01 TO 0.2% CARBON, NICKEL UP TO 4%, CHROMIUM 9-15%, COBALT 3-15%, ONE OR MORE MATERIALS SELECTED FROM THE GROUP CONSISTING OF TUNGSTEN AND MOLYBDENUM UP TO 2%, ONE OR MORE MATERIALS SELECTED FROM THE GROUP CONSISTING OF NIOBIUM AND TANTALUM 1-3% AND IN EXCESS OF THE TOTAL MATERIAL OR MATERIALS SELECTED FROM THE GROUP CONSISTING OF TUNGSTEN AND MOLYBDENUM, VANADIUM UP TO 3%, BORON UP TO 0.05%, NITROGEN UP TO 0.1%, ALUMINUM UP TO 0.1%, AND THE BALANCE ESSENTIALLY IRON. 